Conventionally, technologies that allow user terminals such as mobile phone terminals to carry out data communications during movement (i.e. mobile wireless data communication technologies) have been developed, and therefore technological innovation for various wireless communication systems have been made for practical use. Recently, the fourth-generation communication standards for high-speed data communications, e.g. LTE (Long Term Evolution) system and WiMAX (Worldwide Interoperability for Microwave Access) system using OFDMA (Orthogonal Frequency Division Multiple Access) technology, have become prevalent as mainstream technologies.
In addition, communication procedures using CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism, wireless LAN communication system, have been developed as the basis for communications between base stations and information terminals such as PC (Personal Computer). Then, the IEEE802.11 Working Group, which has developed wireless LAN communication standards, starts to study how to apply OFDMA technology to the current wireless LAN communication system with CSMA/CA mechanism in order to achieve more-efficient data communications.
TDD (Time Division Duplex) type OFDMA system such as WiMAX will be a reference as to apply OFDMA technology to wireless LAN. It transmits and receives data at different timings on the same frequency channel. The WiMAX system may operate under environments without other wireless communication systems causing radio interference in the frequency band of which only the WiMAX system is operated by a single common carrier. According to the basic frame configuration of WiMAX, downlink data frames for transmitting data in directions from base stations to wireless terminals and uplink data frames for transmitting data in directions from wireless terminals to base stations are used for transmission and reception using certain frame lengths, certain numbers of sub-channels, and certain transmission periods.